BEIJING: China, the world´s biggest polluter, unveiled plans on Tuesday for a national carbon market likely to become the world´s largest exchange for emissions credits.Environmentalists praised the move as an important step in the battle against climate change as China burns more coal than any other country, giving it the ignominious title of top greenhouse gas emitter. Although the long-delayed emissions exchange scheme will initially cover just the power generation sector, it is expected to surpass the European Union´s carbon market, currently the world´s biggest. ?The purpose of this programme is to reduce greenhouse gas emissions,? said Zhang Yong, vice chairman of China´s National Development and Reform Commission. The country is the largest investor in renewable energy but has faced an uphill battle transitioning from coal, which is used to generate roughly three-quarters of its power according to the International Energy Agency.